Thermoformable element and use thereof

ABSTRACT

The thermoformable element comprises a strip (1) formed from two layers of foam (2, 3) of a thermoplastic polymer. The layers are welded to one another along their longitudinal edges so as to form a space between them in the shape of a channel (4). The inlet for the channel can be controlled by a non-return valve (6) whereas the exit can comprise a plug (7). The element is thermoformed by circulating a fluid heated to 130° to 140° C. through the channel until the foam becomes soft.

BACKGROUND OF THE INVENTION

The present invention relates to thermoformable elements, of the kindcomprising two adjacent layers of polymers at least one of whichcomprises an elastically compressible foam, at least one of the layersbeing made of a thermoplastic polymer, and to a use of such element.

The use of thermoplastic polymer foams, in particular polyethylene, hasalready been proposed in the medical field, particularly as anorthopaedic support for immobilising fractured limbs. To this end, thefoam is heat-moulded around the part of the body to be bandaged. Foamsof this type have also been used to fit a prosthesis to an amputatedlimb. To this end, the foam is heated to its thermoforming temperaturewhich is approximately between 130° and 140° C. and is applied to thepart of the body to which it is to be fitted, by modelling it until ittakes the form of that part of the body.

Other applications for the foam have been proposed, in particular inEuropean Pat. No. A 2 0 004 829, in which the foam is associated with anelectric heating body in order to enable moulding of the foam, a roughcast of which has been made previously for fitting closely anon-extensible, in particular rigid, casing, to a part of the humanbody.

Although the association of an electric heating body is possible in thecase of an industrial item which, by definition, is mass produced withthe same dimensions, this solution is difficult to adapt for medicaluse, in particular orthopaedic use, in that each bandage not only has tocorrespond to the shape and size of the patient, but also to thefracture or fractures, as well as to the location thereof. In view ofthese constraints, it would be inconceivable, in practice, to makeelectric heating bodies dimensioned according to the size of eachbandage, since this solution would lead to a multiplicity of heatingbodies, and to form them in such a way as to produce homogeneous heatingacross the entire surface of the bandage, which is extremely difficultto carry out and has to be studied from case to case. This condition isof great importance for thermoforming since foams of this type have verypoor thermal conductivity, so that the density of current per section ofheating body has to be as constant as possible for each portion of thefoam surface to be thermoformed.

For this reason it has been proposed to make orthopaedic supports usingthermoformable materials without incorporating heating means therein.The orthopaedist cuts pieces of thermoformable materials to the requireddimensions or buys elements which are sold ready cut, heats them in anoven or in a hot water bath according to the thermoforming temperatureof the material used and then forms it on the patient. An orthopaedicbandage of this type is described in French Pat. No. 1 570 760. In thiscase, a sheet of a thermoplastic material which is rigid at roomtemperature is inserted between two sheets of a foam made ofthermoplastic material, in order to provide support for the limb to beimmobilised.

In French Pat. No. 2 120 515 a splint has also been proposed whichcomprises a rigid shell the inner face of which is lined with a type ofimpervious cavity formed by a flexible casing. A fluid or material whichcan be hardened can be injected into the cavity in order to immobilisethe limb inside the rigid shell. A solution of this type is difficult toproduce on an industrial scale in that different sizes of shell have tobe produced, the shell having unchangeable dimensions.

Another factor which should be considered in thermoforming is thecompatibility of the thermoforming temperature with what the skin canwithstand. In the case of flexible foams, such as those used for examplein French Pat. No. 1 570 760, their low density makes it possible towithstand a relatively high thermoforming temperature. On the otherhand, in the case of denser materials, for example materials which arerigid at room temperature, a temperature of 50° to 60° C. cannot beexceeded if the technique of heating in an oven is used and if thematerials are to be applied around the limb to be immobilised whilstthey are still soft. This has made necessary the development of specialmaterials for this application which are very expensive, so that theiruse is restricted as a result.

The object of the present invention is to provide a theremoformableelement which ensures even heating of the entire surface of the form tobe thermoformed, whatever the shape or size of the surface.

SUMMARY OF THE INVENTION

The present invention resides in a thermoformable element comprising twoadjacent layers of polymers one of which at least one compriseselastically compressible foam, and at least one layer is made of athermoplastic polymer, characterised in that the edges of the layersdefine between them an enclosed space connected to the outside by atleast two openings one of which comprises an inlet for a fluid forheating the said thermoplastic polymer to its thermoforming temperatureand the other of which comprises an outlet for this fluid.

The invention has many advantages. The heating fluid can circulateacross the entire surface to be heated and thus heat it evenly. Theelement can be made for example in the form of a very long strip and cutto the required length according to the bandage to be made. Heating thebandage internally means that because of the large drop in temperaturethrough the layers of foam, the element can be thermoformed without itsouter surface that makes contact with the skin, reach a temperature muchgreater than that of the human body. Consequently, it is possiblewithout further steps to use inexpensive thermoplastic polymer which arecommercially readily available. The enclosed space in which the heatingfluid circulates can also be used to circulate a cooling fluid, inparticular to accelerate foam hardening after the thermoformingoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become apparent fromthe following description and the attached drawings which illustratediagrammatically and by way of example only thermoformable elementsembodying the present invention. In the drawings:

FIG. 1 is plan view of a first embodiment.

FIG. 2 is a section along II--II of FIG. 1.

FIG. 3 is a section of a bandage made using this embodiment.

FIG. 4 is a perspective view of a second embodiment.

FIG. 5 is a plan view of a third embodiment.

FIG. 6 is a section along line VI--VI of FIG. 5.

FIG. 7 is a perspective view of a fourth embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 and 2 illustrate a strip 1 comprising two layers of foam 2 and 3made of a thermoplastic polymer, in particular low density polyethylene.The layers are welded to one another along their two longtudinal edgesin such a way as to form between them a space in the form of a channel4. This welding operation can be performed by ultrasonic thermal weldingin particular. The two longitudinal edges of the layers of foam 2 and 3can also be stuck together using, for example, a contact type adhesive.FIG. 2 shows that the cross section of the strip 1 preferably has theshape of a rectangular parallelogram, in order to facilitate the joinbetween the two adjacent longitudinal edges when the strip 1 is wound inthe manner of a spiral around a generally cylindrical part of the humanbody. One of the outer facs of the strip 1 is preferably coated with aself-adhesive substance.

The channel 4, when not in use, is in the form of a single slot, the twowalls of which can be moved apart from one another when a fluid underpressure is passed between the two layers of foam, as will be explainedlater. The strip 1 can be produced in a continuous manner and packagedin the form of rolls each formed from a strip several metres in length.The strip can then be cut to the required length according to thebandage to be made.

In order to thermoform the bandage around the fractured limb, a hotfluid is passed under pressure through the channel 4. The walls of theslot move apart to allow the passage of the fluid. The fluid can be, forexample, hot air or water vapour the temperature of which isapproximately 130° to 140° C., which is the thermoforming temperature ofthe foam forming the layers 2 and 3. The fluid emerges at the other endof the channel 4. The foam softens gradually. When it is sufficientlysoft, the temperature on the outer surface of the strip is approximately40° C. The passage of the fluid through the channel 4 is then stoppedand the bandage is formed by winding the strip 1 around the fracturedlimb, tightening it sufficiently so that the strip adopts the shape ofthat part of the body. The bandage is then left to cool and can then becovered with plaster (FIG. 3) or a shell 5 made of thermoplasticmaterial, which is also fitted by thermoforming around the bandage. Theshells are usually made from polypropylene strips.

The thermoforming temperature of polypropylene is approximately 200° to240° C., but the foam bandage acts as an insulator which prevents thepatient from being burned, so that the shell can be formed directly insitu. However, in order to prevent the polyethylene foam from meltingduring moulding of the polypropylene shell, a cooling fluid canadvantageously be passed through the channel 4. The fluid is used toprotect both the foam and the patient. The channel 4 thus also enablesthe moulding of the propylene shell 5 on the patient, which is a greatsimplification. Shells of this type could not hitherto be made ofpolypropylene in situ because of its high thermoforming temperature;instead, it was necessary to use acrylic type materials such as thatwhich is known under the registered trademark orthoplast, the price ofwhich is much greater than that of propropylene.

As illustrated in FIG. 1, after cutting the strip 1 to the requiredlength, its two ends can be provided with a non-return valve 6 at theinlet and a plug 7 at the outlet. During the heating operation tothermoform the strip 1, the plug 7 is open. The pressure loss which itcauses ensures even distribution of the heating fluid in channel 4.

A certain amount of time after the formation of the bandage formed bythermoforming the strip 1 and the placing of shell 5 applied around thebandage, the muscles of the immobilised part of the body atrophy, sothat clearance is created between that part of the body and the bandage.The clearance can be taken up by injecting a fluid under pressure intothe channel 4 of the strip 1, after closing the plug 7. The wall of theslot comprising the channel 4 move apart and the clearance is thuseliminated. The pressure thus produced around the bandaged part of thebody can moreover be adjusted by the patient or by the doctor. To ensureproper imperviousness of the space between the foam layers, animpervious film such as PVC film can be applied to the internal faces ofthe foam layers 2 and 3. A proper air chamber could also be disposed inthe channel 4 to which the valve 6 and the plug 7 would be secured, e.g.by adhesion or by heat welding.

The invention is not limited to the embodiment of which thethermoformable element is in the form of a bandage. As shown in FIG. 4,the bandage can also be in the form of a rough cast of a part of thebody, for example the leg or knee. The basic idea, however, remainsidentical to that of the strip. The bandage 8 in FIG. 4 comprises twolayers of foam 9 and 10 welded or stuck together on their respectiveedges, and forming an enclosed space 11. In this embodiment, the bandage8 is provided with a non-return valve 12 and four plugs 13. Theprinciple is identical to that of the strip 1. A hot fluid between 130°and 140° C. is passed through the valve 12 and emerges via the openingsof the plugs 13. The rough cast heated in this way to the thermoformingtemperature is then applied around the leg of the patient; care istaken, in particular, to mould closely the pressure points below theknee, above the fracture to allow a support (not shown) to be associatedwith the bandage. As in the case of the previous embodiment, a rigidshell made of plaster or polypropylene in particular can be formedaround the bandage 8. In the case of forming the shell of polypropylenein situ, a cooling fluid can also be passed in the space arrangedbetween the two layers of foam 9 and 10, as described above.

Polyethylene foams with closed pores have the property of returning totheir original shape when they are reheated to their thermoformingtemperature, so that the bandage can be thermoformed several times insuccession if it proves to be necessary to change the immobilisationposition of the limbs.

The above description illustrates the extreme flexibility in use of thethermoformable element which is the subject of the invention both in itsstrip form and in the form of a preformed sleeve in FIG. 4. In thelatter case, it can be seen that different sizes of sleeve can be madeindustrially to allow fitting for the entire population. Thethermoformable element also simplifies the work of the orthopaedist inthat it is no longer necessary to make a preform of the leg or arm inorder to make a moulding structure, since all the moulds, that of thebandage and the shell surrounding the bandage, can be made directly insitu. The means for heating the thermoformable element also eliminatesany risk of burning. The space between the layers of foam can be usednot only for heating, but also for cooling and by closing it at itsinlet or outlet(s) can be used to hold a fluid under pressure to fill upthe clearances due to atrophy of the muscles. To this end, the fluidused can also be a gel.

In the case where the thermoformable element is in the form of a flat orpreformed rough cast of the type of that in FIG. 4, the rigid shellpreferably comprises directly the outer layer 9 of the bandage 8.Advantageously, the outer layer 9 which is ridig at room temperature canbe made from a sheet of ethylene-vinyl acetate co-polymer 3.2 mm thick,such as that sold under the trade name "Worblex Electra® 7013" byGurit-Worbla AG in Ittigen in the canton of Bern (Switzerland). Thisproduct has a density of 1.16 kg/dm³ at 23° C. and a VICAT softeningpoint at 73° C. The foam which is associated with it as an internallayer 10 comprises a sheet of polyethylene reticulated by irradiation of4 mm thickness with a density of 67 kg/m³ and the thermoformingtemperature of which is approximately 120° C. The foram is sold inparticular under the trademark Alveolit® 1500 by Alveo AG in Lucerne(Switzerland).

In a case of this type where the two layers 9 and 10 are made ofmaterials which cannot be heat welded, the edges of the adjacent layersare secured to one another by sticking using a contact adhesive, bystitching or by an adhesive strip 19 (FIG. 6) in particular. If the twolayers are of the same material or of two materials which can be weldedtogether at their softening temperature, the edges of the layers can bewelded as already stated. However, with heat weldable materials of thistype it is then necessary, if the element is to be thermoformed severaltimes, to spread talc or magnesia inside the enclosed spaced definedbetween the two layers in order to prevent their sticking when thethermoforming takes place.

In the case of relatively extensive surfaces, it is necessary to takesteps to provide even irrigation of the entire space by the heatingfluid. As illustrated in FIGS. 5 to 7, the steps consist firstly inarranging an inlet opening 14 near to the edge of the enclosed spaceddefined between the adjacent layers 9 and 10, the cross section of whichis substantially greater than that of the outlet opening(s) 15, in sucha way as to cause pressure loss. The second step consists in arrangingirrigation channels 16 in the thickness of one of the layers connectingthe inlet opening 14 to the outlet opening(s) 15. The channels 16 have,in this example, a cross section of approximately 1 mm². The object ofthese is to distribute the heating fluid under pressure across theentire surface of the enclosed spaced. Since the pressure loss occurs atthe outlet of the fluid under pressure, the adjacent layers 9 and 10, atleast one of which is elastically deformable, are forced apart from oneanother so that the fluid is distributed between the channels and thusirrigates the entire space, producing even heating of the adjacentlayers 9 and 10 at their thermoforming temperature. It is not necessaryfor each irrigation channel 16 to terminate in an outlet opening, it isalso useful to arrange intermediate irrigation channels 16a which do notterminate in any outlet. The distance between the irrigation channels 16or 16a is approximately 10 cm.

In the case where a large surface is to be formed, for example in thecase of a corset, it can be advantageous to provide ventilation for thefoam surface in contact with the skin either directly or preferably byinterposing a knitted fabric 18. As shown in FIG. 7, ventilation occursby means of channels 17 arranged in the thickness of the inner layer 10and arranged so as to occupy a substantially vertical position so thatthe air circulates by the chimney effect. The presence of a knittedfabric 18 between the foam 10 and the skin means that the suction effecton the skin, similar to that of a suction cup, can be avoided orreduced. This enables, in particular, channels 17 of sufficient crosssection to be arranged to provide good air circulation. 3×3 mm channelsachieve good results. If there is no provision for the presence of aknitted fabric, the cross section of the channels can be reduced toapproximately 1×1 mm.

According to a modification which is not shown, instead of using twolayers which are welded, stuck, stitched together or secured by anadhesive strip 19 (FIG. 6), the layers could be formed by compressionmoulding a tube of extruded foam. In a case of this type, the two layersare of necessity made of a foam of the same material, so that the insidehas to be coated with talc to prevent sticking during thermoforming.

Another modification is also be possible in which the outer layercomprises neither flexible foam nor a material which is rigid at roomtemperature, but an elastic knitted fabric impregnated with PVC to makeit impervious, the inner layer being made of a foam of a thermoformablematerial secured to the knitted fabric according to one of theabove-mentioned securing methods in order to arrange an enclosed spacebetween their edges. A knitted fabric of this type can be used forexample to closely bind an ankle by means of lacing, the thermoformingof the foam enabling the pressure of the elastic knitted fabric to bedistributed evenly.

As has been stated above, the means for heating the thermoformableelement according to the invention comprises a hot fluid passed into theenclosed space arranged between the two layers of the element. Accordingto one modification, it is also possible to heat flat products madeusing, for example, a layer of rigid polyethylene 9 and a layer ofpolyethylene foam 10 (FIG. 5) with closed pores by introducing coldwater into the enclosed space arranged between the two layers. The watercan be introduced by connecting the outlet opening 14 (FIGS. 5 and 6) toa mains water tap or likewise by wetting the element in a basin ofwater. In the latter case, the water distribution can be improved by thepresence of a hydrophilic layer, such as cotton wool, between the layersof polyethylene. The element is then placed in a microwave oven wherethe water is heated, is transformed into steam and emerges from theenclosed space via openings 14 and 15, heating the enclosed space andimparting the heat to the layers 9 and 10 from inside the element, inexactly the same way as steam or hot air under pressure.

It may also be pointed out that, in the case of large surfaces, pointsor lines can be provided for securing the two layers inside the enclosedspace in order to prevent one layer from sliding relative to the other.

Although the invention has been described in particular in connectionwith its use as an orthopaedic bandage, other applications of theinvention are also considered as being covered by the protective scope.Thus an element of this type can be used as a thermoformable sealingjoint, a thermoformable mattress for burns, car seats, etc.

We claim:
 1. A Thermoformable element comprising two adjacent layers ofpolymers one of which at least comprises elastically compressible foam,and at least one layer is made of a thermoplastic polymer, which twolayers are united at the edges of the layers so as to define between thelayers an enclosed space, and in which at least two openings areprovided for connecting the said space to the exterior of the elements,one of which openings comprises an inlet for a fluid for heating thesaid thermoplastic polymer to its thermoforming temperature and theother of which openings comprises an outlet for this fluid.
 2. Anelement according to claim 1, characterised in that both said layers aremade of a thermoplastic polymer foam.
 3. An element according to claim1, characterised in that one of the said layers is made of athermoplastic material which is rigid at room temperature.
 4. An elementaccording to claim 1, further including a non-return valve and a plugrespectively controlling the said inlet and outlet openings.
 5. Anoutlet according to claim 1, characterised in that the said edges aresecured to one another by heat welding.
 6. An element according to claim1, further including an impervious film associated with the adjacentfaces of the said layers.
 7. An element according to claim 1,characterised in that it is made in the form of a strip formed from twolongitudinally welded layers.
 8. An element according to claim 1,characterised in that one of the outer faces of the element isself-adhesive.
 9. An element according to claim 1, characterised in thatone of the said layers is made of an elastically extensible material.10. An element according to claim 1, characterised in that the crosssection of the inlet opening is greater than that of the outlet opening.11. An element according to claim 1, characterised in that one of thefaces forming the said enclosed space is provided with irrigationchannels beginning at the inlet openign and distributed evenly acrossthe surface on which the heating fluid is to be distributed.
 12. Athermoformable element comprising two adjacent layers of polymers one ofwhich at least comprises elastically compressible foam, and at least onelayer is made of a thermoplastic polymer, characterised in that theedges of the layers define between them an enclosed space connected tothe outside by at least two openings one of which comprises an inlet fora fluid for heating the said thermoplastic polymer to its thermoformingtemperature and the other of which comprises an outlet for this fluid,wherein said inlet and outlet openings are controlled respectively by anon-return valve and plug.
 13. A thermoformable element comprising twoadjacent layers of polymers one of which at least comprises elasticallycompressible foam, and at least one layer is made of a thermoplasticpolymer, characterised in that the edges of the layers define betweenthem an enclosed space connected to the outside by at least two openingsone of which comprises an inlet for a fluid for heating the saidthermoplastic polymer to its thermoforming temperature and the other ofwhich comprises an outlet for this fluid, wherein the cross-section ofthe inlet opening is greater than that of the outlet opening.
 14. Athermoformable element comprising two layers of polymers adjacent faceto face and having complementary outlines one of which at leastcomprises elastically compressible foam, and at least one layer is madeof a thermoplastic polymer, in which two layers are sealed along saidoutlines so as to define between them a sealed slot, and in which atleast two spaced openings are provided for connecting the said slot tothe exterior of the elements, one of which openings comprises an inletfor a pressurized fluid the pressure of which being such that it movesapart said layers from one another to form an air-tight space betweensaid layers and the other of said openings comprises an outlet for thisfluid, which is a fluid for heating the said thermoplastic polymer toits thermoforming temperature.
 15. A thermoformable elementcomprisingfirst and second layer means for containing a fluid, saidlayer means being sealably affixed one to the other at the peripherythereof so as to define a single sealed space therebetween; inlet meansfor allowing said fluid to pass from outside said layers to said spacebetween the layers; and outlet means for allowing said fluid to passfrom within said space to the outside, wherein said first layer means isa thermoplastic polymer and said second layer means is an elasticallycompressible foam and wherein said fluid may be passed through saidspace within the element so as to heat said thermoplastic polymer layerto its thermoformable temperature.